The present invention relates to a process for producing bromomethylated polyphenylene ethers, and to the resultant ethers.
The polyphenylene ethers (PPE) produced according to U.S. Pat. Nos. 3,306,874 and 3,306,875 or also according to German Patent Application No. P 33 13 864.8, corresponding to U.S. Ser. No. 582,711, preferably from alkyl-substituted phenols, and using complex-forming agents, e.g. copper bromide and dibutylamine, under oxidizing condensation, are well-known compounds utilized especially in synthetic-resin blends and exhibiting a great variety of properties depending on the starting materials, substituents, co-condensates, or mixtures.
The literature, for example DAS's Nos. 2,009,065 and 2,047,613, discloses lists which include the bromomethyl group among many different substituents possible for polysubstituted polyphenylene ethers, but the only specific bromomethylated ether disclosed is poly(2,6-dibromomethyl-1,4-phenylene)ether. No example is disclosed for preparing this ether, nor is a general method disclosed for preparing bromomethylated polyphenylene ethers.
In contrast thereto, a large number of publications, including, e.g., DAS's Nos. 2,037,510 and 2,616,746, disclose halogenated polyphenylene ethers. These references require, in the case of a halogenated hydrocarbon residue as the substituent, at least two carbon atoms between the halogen atom and the phenol nucleus, and describe as remote the possibility of inserting bromomethyl groups.
Bromomethylation per se is a well-known reaction of aromatic compounds. A compilation can be found in Houben-Weyl, "Methoden der organischen Chemie" (Methods of Organic Chemistry), V/4: 484-487 (1960). However, page 487 teaches that phenols evade this fate by polycondensation with formaldehyde. Since this known, and here entirely undesirable, phenolic resin formation also occurs with phenol ethers, as disclosed in, e.g., "Kunststoff-Handbuch" (Plastics Manual), X: 22, Carl Hanser Publishers, 1968; and "Ullmanns Encyklopaedie der technischen Chemie" (Ullmann's Encyclopedia of Technical Chemistry) 4th ed./1979, 18:248, it was unexpected that PPE could be reacted with formaldehyde without undesirable crosslinking.
It is also surprising that bromomethylation of PPE can be performed with good conversion rates even if the polymeric material is insoluble or only sparingly soluble in the carboxylic acids, e.g., acetic acid or propionic acid, used in the present process.
Finally, it is known that ethers can be cleaved by means of hydrogen halides. Inasmuch as bromomethylation presupposes the presence of considerable amounts of hydrogen bromide, it is unexpected that reaction of PPE can take place with minimal to negligible cleavage.
In summation, everything was prejudicial to any expectation of success of the process of the invention.